Architecturally heterogeneous multi-material multi-principal element alloy (MPEA) composites represent a unique class of heterostructured materials with great potential to evade the strengthductility trade-off dilemma. However, most conventional processing routes involving high temperatures (e.g., casting, additive manufacturing, and powder metallurgy) suffer from various metallurgical issues such as excessive elemental diffusion, segregation, hard intermetallic phase formation, cracking, and poor densification. To mitigate these challenges, the project suggests prefabricating various MPEA powders into billets using cold spraying (CS) and then employing solid-state friction stir processing (FSP) to achieve microstructural densification. This approach will initiate various dynamic recrystallizations in different compositional domains, allowing us to engineer architecturally heterogeneous multi-material MPEA composites. In general, this project will be implemented in phases, including optimizing process, controlling the heterostructure, evaluating mechanical performances from ambient to cryogenic temperatures, and elucidating deformation mechanisms. The results can be expected to build up the processingmicrostructuremechanical behavior correlations of the newly developed multi-material MPEA composites in a quantitative manner. This will facilitate the design and fabrication of similar heterostructured composites, thereby impacting a wide range of industrial sectors, e.g., transport, defense, nuclear, and manufacturing.